The double glazing of windows is well known for the purpose of heat insulation and to reduce solar heat loads, and it is known to add a tinted, reflective or the like pane to an existing clear glass pane. Various methods and means for accomplishing such retroglazing have been proposed, some of which have been commercially used, among which, for example, have been methods and means in accord with U.S. Pat. Nos. 3,971,178, 2,684,266 and 3,928,953. Reference may be had also to U.S. Pat. Nos. 3,226,903; and 3,105,274.
Taught by such patents are arrangements in which a hollow metal spacer member containing a desiccant is sealed to a peripheral portion of a surface of a new pane which is applied to an existing pane in a window sash. The spacer may comprise a slit therealong through which the desiccant is exposed to the dead air space between the two panes in the completed installation. U.S. Pat. No. 3,226,903 suggests that silica gel be inserted into the spacer and the spacer then be held in dry heated condition until the installation is to be completed. U.S. Pat. No. 3,928,953 relates to the sealing together of two new panes at the factory, with the desiccant open to the sealed space between the two new panes until they are separated in preparation for final installation. U.S. Pat. No. 3,971,178 suggests substitution of a strippable overlay of sheet material against the exposed side of the spacer in a prefabricated subassembly comprising only one pane of glass.